Problema Solution
a 20lb bag of cement mix contains 20% cement and 80% sand. How much pure cement must be added to produce a cement mix that is 40% cement?
Answer provided by our tutors
let x = lbs of pure cement that needs to be added
20% of cement in the 20 lbs + 100% of cement in x lbs = 40% cement in the total mix (20 + x)
0.20*20 + 1.00*x = 0.40(20 + x)
by solving we find
x = 6.67 lbs
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6.67 lbs of pure cement must be added.